In the field of digital communications, transmission of voice, images, audio, and videos is needed in a wide range of applications such as a mobile phone call, an audio/video conference, broadcast television, and multimedia entertainment. Audio is digitized, and is transmitted from one terminal to another terminal by using an audio communications network. The terminal herein may be a mobile phone, a digital telephone terminal, or an audio terminal of any other type, where the digital telephone terminal is, for example, a VOW telephone, an ISDN telephone, a computer, or a cable communications telephone. To reduce resources occupied by a speech/audio signal during storage or transmission, the speech/audio signal is compressed at a transmit end and then transmitted to a receive end, and at the receive end, the speech/audio signal is restored by means of decompression processing and is played.
In current multirate speech/audio coding, because of different network statuses, a network truncates bit streams at different bit rates, where the bit streams are transmitted from an encoder to the network, and at a decoder, the truncated bit streams are decoded into speech/audio signals of different bandwidths. As a result, the output speech/audio signals switch between different bandwidths.
Sudden switching between signals of different bandwidths causes obvious aural discomfort in human ears. Besides, because updating of states of filters during time-frequency transform or frequency-time transform generally requires the use of a parameter between consecutive frames, when some proper processing is not performed during bandwidth switching, an error may occur during the updating of these states, which causes some phenomena of abrupt energy changes and deterioration of aural quality.